PANTOGRAPH

CATENARY WIRE

SMOTHING REACTOR

The pantograph is employed in railways for collection of current where the operating speed is as high as 100 or 130 Kmph and the current to be collected are as 2000 or 3000 amperes.

Pantograph are mounted on the roof of the vehicles and usually carry a sliding shoe for contact with the overhead trolley wire.

These consist of a jointed frame usually of steel tubing.

The contact shoes are usually about 1.2 meters long.

Pantograph collector maintain link between overhead contact wire and power circuit of the electric locomotive at different speed under all wind conditions and stiffness of overhead equipment.

This necessities that positive pressure must be maintained at all times to avoid lass of contact ad sparking but the pressure must be as low as possible so that wear of overhead contact wire is minimum.

1) It can be operate in either direction of motion.2) There is no risk of leaving wire junction etc.3) The erection of the overhead network is very

simple due to absence of points and grooved crossings required for bows.

4) Its height can be varied from the driver’s cabin by carrying out simple operations.

Since in railways a sliding current collector is employed, therefore, the contact wire is required to be suspended with very small sag so that the contact between the wire and collector may be maintained at high speed.

For such short spans an indirect method of suspension is adopted, in which the trolley wire is supported by another wire known as the “Catenary” or “Messenger” wire and is fixed with considerable sag between supports at suitable distance.

The wire is usually made of more than seven strands of steel.

To avoid the use of insulated droppers the whole of the messenger wire is usually insulated, and it may therefore be used if required for carrying current.

The position of contact wire remains practically constant at all temperatures which may cause large amount of sag in the catenary wire.

Now a days the catenary construction employed is of either the single catenary or compound catenary.

In single catenary construction, a steel wire with 7 or more strands supports the trolley wire by means of droppers clipped to catenary and trolley wire at equidistant horizontal intervals.

The span of catenary wire may be from 45 to 90 meters with a sag of from 1 to 2 meters respectively for straight track.

The distance of droppers is between 3 and 5 meters.

Such construction provides sufficient flexibility for speeds upto 120 kmph without any problem of current collection.

Besides this it is relatively cheaper, easy to erect and does not require heavy maintenance.

Single catenary construction is considered suitable for most light weight ac systems and for branch and loop lines and secondary routes where traffic density is low and operating speeds are low.

The compound catenary construction is employed for heavy current i.e. where traffic density is high.

It consist of three wires, all in the same vertical plane.

The upper wire is catenary wire, which is insulated from the supporting structures.

From this wire another wire, known as “intermediate catenary”, is supported by droppers clipped to both wires.

The third wire i.e. trolley wire is maintained in definite and constant tension by means of automatic tightening gear.

Both contact and catenary wires are divided in sections of 150 meters and each section is anchored at the centre.

The purpose of intermediate catenary besides increasing the current carrying capacity is to provide more uniformity in elasticity.

The smoothing reactor is used to make a.c. ripple free d.c. available from rectifire and pure d.c. is given to d.c. series motor better performance.

When the thyrister is used to rectify from AC to DC, the sinusoidal wave display on the voltage and time graph is confined to above the positive axis.

In order to create a steady supply of voltage and smoothen the delivery, a smoothening circuit is connected.

The smoothening circuit may include inductors and capacitors .

Thank you